Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.81	6.635%	$91.5035	$91.50	$91.50	$91.50
Purchase #2	$49.89	10.669%	$55.2128	$55.21	$55.20	$55.20
Purchase #3	$12.29	11.609%	$13.7167	$13.72	$13.70	$13.70
Purchase #4	$215.95	11.555%	$240.903	$240.90	$240.90	$240.90
Purchase #5	$50.26	5.567%	$53.058	$53.06	$53.05	$53.10
Purchase #6	$181.98	7.861%	$196.2854	$196.29	$196.30	$196.30
Purchase #7	$194.59	9.113%	$212.323	$212.32	$212.30	$212.30
7 purchase totals =	$790.77		$863.0024	$863.00	$862.95	$863.00